A class of diseases are caused by mutations involving the expansion of triplet sequence repeats. These disorders are called trinucleotide repeat diseases. Several trinucleotide repeat diseases have CAG as the repeated sequence. Since CAG codes for the amino acid glutamine, these CAG repeat disorders are known as polyglutamine diseases. Polyglutamine diseases include Spinobulbar muscular atrophy, Huntington disease, Dentatorubral-pallidoluysian atrophy, Spinocerebellar ataxia type 1, Spinocerebellar ataxia type 2, Spinocerebellar ataxia type 3, Spinocerebellar ataxia type 6, Spinocerebellar ataxia type 7, and Spinocerebellar ataxia type 17.
Huntington's Disease (HD) is a neurodegenerative disorder caused by an expansion of a CAG triplet repeat sequence in the huntingtin gene. This expansion results in the expression of the huntingtin protein with an extended polyglutamine region that misfolds and causes the demise of specific cells in the brains of HD patients.
Effective treatments are needed for Huntington's Disease as well as other polyglutamine diseases.